1. Field of the Invention
This invention relates to an integrated process for the production of food, feed and fuel from biomass. More particularly, the present invention is directed to an improved process wherein the carbohydrate fractions of biomass are converted into protein-rich food for humans, protein-rich feed for animals and liquid fuel such as ethanol. On the other hand, the lignin fraction can be converted into adhesives, various chemicals or can be used as a burning fuel.
In the following description, concentrations of substances are expressed as wt/vol (weight per unit volume of total mixture), as vol/vol (volume per unit volume of total mixture), as wt/wt (weight per unit weight of total mixture on a dry basis).
The term biomass used herein includes lignocelluloses, which are mostly derived from crop residues, wood and wood residues. Generally speaking, biomass can be fractionated into cellulose, hemicelluloses and lignin. It is the most important source of organic carbon that can be used for bioconversion into food, feed and fuel. The term biomass also includes solid and liquid manures.
2. Description of Prior Art
In view of the world supply and demand of calories and proteins, the development of unconventional sources of food and feed is considered to be most important for mankind. Heavy demands of grain for the production of ethanol fuel would further aggravate present shortages. Moreover, escalating food/feed prices throughout the world have established the need for a high energy feed (70-75% digestability). It has already been proposed to produce high energy feed from poplar, and recently renewable biomass (especially forest biomass) has been found to be very attractive feedstock for the production of food, feed and also ethanol fuel.
The forest is a very important renewable wealth and forest biomass is produced in large quantities every year throughout the world. Similarly, large quantities of mill and logging residues are also available.
The biomass of plant origin, generally called lignocelluloses, contains 45-56% cellulose, 10-29% hemicelluloses, and 14-30% lignin. It would,therefore, appear that bioconversion of carbohydrates (75-50%) into animal feed rich in protein (40-47%) would save millions of dollars which are presently spent to import soybean as a source of protein to supplement animal feed. On the other hand, the composition of biomass of manures of animal origin varies considerably depending on the feed given to the animal. Usually, this source is rich in starch lipids, protein and microbial biomass, and also contains little cellulose, hemicelluloses and lignin. Similarly, the affluents from food factories are rich in starch, protein and minerals but contain very little cellulose, hemicelluloses and lignin.
In an article entitled "In Search of Microbial Food and Feed: Chaetomium cellulolvticum--the Obvious Answer", which I presented at the Symposium "New Sources of Food" of the National Meeting of AICHE at Denver, Col., Aug. 28-31, 1983, I indicated that the production of single cell protein SCP from biomass with Chaetomium cellulolyticum seems to be more promising than all the other microorganisms being tried in the world. C. cellulolyticum is a new fungus which I discovered in 1972 and is deposited at the ATCC under accession number of 32319. The taxonomy, morphology and physiology of this new fungus were reported in Mycologia, 68:600-610, 1976.
A few processes have been proposed or used to convert "lignocellulosic biomass" into protein-rich feed for humans and animals. However, they suffer with one or more of the following drawbacks.
1. In most cases the "lignocellulosic biomass" is pretreated with various processes to make it suitable for bioconversion into protein-rich feed by fermenting with various microorganisms. During these pretreatments lignin is to be removed; however, by doing so, almost all the hemicelluloses, which are a potential source of carbohydrates, are also removed. These hemicelluloses end up in a waste stream which creates pollution problems because of its very high Biological Oxygen Demand(BOD).
2. Most of the microorganisms used in such processes have poor conversion efficiency and a considerable amount of lignocelluloses are left utilized which cannot be separated from the final product thus lowering its value as protein supplement because of low protein content of the final product.
3. Some of the organims such as Chaetomium cellulolyticum ATCC 32319, being used in some processes for production of protein-rich feed for animals, has recently been found to produce toxic compounds.
The following Patents deal with a simple treatment of biomass with the known microorganism, Chaetomium cellulolyticum ATCC 32319.
U.S. Pat. No. 4,379,544 PA1 U.S. Pat. No. 4,401,060 PA1 U.S. Pat. No. 4,447,530 PA1 U.S. Pat. No. 4,526,791 PA1 Canadian Patent No. 1,124,131 PA1 Canadian Patent No. 1,129,709 PA1 Chaetomium cellulolyticum IAF-101 (NRRL 18756) PA1 Aspergillus sp. IAF-201 (NRRL 18758) PA1 Penicillum sp. IAF-603 (NRRL 18759) PA1 Trichoderma reesei QMY-1 (NRRL 18760)
The disadvantages associated with fuel ethanol production from "lignocellulosic biomass.revreaction. through enzymatic hydrolysis are the following:
1. Cost of enzyme production is very high.
2. Substrate conversion into sugars is low (about 50%).
3. Final concentration of sugars in the hydrolysate is 3-5% which may give 1.5-2.5% ethanol in the fermentation broth. This small quantity of ethanol in the broth is not economical for distillation into 95% ethanol.
4. Hemicelluloses are not properly utilized which end up in pollution stream. Although there are many methods to convert pure xylose (a major component of hemicelluloses into ethanol, none is capable to give more than 40% of theoretical yield from hemicelluloses.